I have checked the LDP-7024, but can not see any MUTE button.
Where is it placed?
I can see these buttons:
Speed, DND, Trans/Pgm, Speaker, Hold/Save, volume.
Is it a programmed button?
To me it seems to be a programmed button (flex key) that gives info about "who has called" (CLIS Calling Line Information Save).
But if you press the button, this will be shown in the display.
///doktor